Method of recording information in optical recording medium, information recording apparatus and optical recording medium

ABSTRACT

It is an object of the present invention to provide an information recording method for recording information in a data rewritable type optical recording medium having a plurality of information recording layers whereby a sufficiently high erasing efficiency can be ensured when data recorded in any one of the information recording layers are directly overwritten. In the information recording method according to the present invention, information is recorded in an optical recording medium  10  having at least a stacked L 0  layer  20  and L 1  layer  30  by projecting a laser beam thereonto via a light incidence plane  13   a . In the case where information is to be recorded in the optical recording medium  10 , information is recorded in the L 0  layer  20  using an off-pulse recording format and information is recorded in the L 1  layer  30  using an on-pulse recording format. As a result, even in the case of directly overwriting data recorded in either of the L 0  layer  20  or the L1 layer  30 , a sufficiently high erasing efficiency can be ensured.

This application is a 371 of PCT/JP03/01550, filed Feb. 14, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to a method of recording information in anoptical recording medium, and particularly to a method of recordinginformation in a data rewritable type optical recording medium having aplurality of information recording layers. Further, the presentinvention relates to an information recording apparatus for recordinginformation in an optical recording medium, and particularly to aninformation recording apparatus for recording information in a datarewritable optical recording medium having a plurality of informationrecording layers. Furthermore, the present invention relates to anoptical recording medium, and particularly to a data rewritable opticalrecording medium.

DESCRIPTION OF THE PRIOR ART

Optical recording media typified by the CD and the DVD have been widelyused as recording media for recording digital data. The recordingcapacity demanded of such optical recording media has increased year byyear, and various proposals have been made to achieve this. One of theseproposals is a technique that uses a two-layer structure for theinformation recording layers contained in the optical recording media,which has found practical application in the DVD-Video and DVD-ROMformats which are read-only optical storage media. With such read-onlyoptical recording media, pre-pits formed on the substrate surface becomethe information recording layer, and such substrates have a laminatedstructure with an intervening intermediate layer.

In addition, in recent years, proposals have been made for opticalrecording media with a two-layer structure for the information recordinglayer to be used also as an optical recording medium in which data canbe rewritten (data rewritable type optical recording medium) (SeeJapanese Patent Application Laid Open NO. 2001-273638). Such a datarewritable type optical recording medium has a structure in which arecording film and dielectric films between which they are sandwichedform an information recording layer, and these information recordinglayers are laminated.

A phase change material is generally used for forming a recording filmof a data rewritable type optical recording medium and data are recordedutilizing the difference in the reflection coefficients between the casewhere the recording film is in a crystal phase and the case where it isin an amorphous phase. More specifically, in an unrecorded state,substantially the entire surface of the recording film is in a crystalphase and when data are recorded, the phase of a predetermined region ofthe recording film is changed to the amorphous phase to form a recordingpit. The phase of the phase change material in the crystal phase can bechanged to the amorphous phase by heating the phase change material to atemperature equal to or higher than the melting point thereof andquickly cooling it. On the other hand, the phase change material in theamorphous phase can be crystallized by heating the phase change materialto a temperature equal to or higher than the crystallization temperaturethereof and gradually cooling it.

Such heating and cooling can be performed by adjusting the power(output) of a laser beam. In other words, it is possible not only torecord data in an unrecorded recording film but also to directlyoverwrite (direct-overwrite) a recording mark already formed in a regionof the recording film with a different recording mark by modulating theintensity of the laser beam. Generally, the power of the laser beam ismodulated in accordance with a pulse waveform having an amplitudebetween a recording power (Pw) and a bottom power (Pb) in order to heatthe recording film to a temperature equal to or higher than the meltingpoint thereof and the power of the laser beam is set to the bottom power(Pb) in order to quickly cool the recording film. Further, in order toheat the recording film to a temperature equal to or higher than thecrystallization temperature thereof and gradually cool it, the power ofa laser beam is set to an erasing power (Pe). In this case, the erasingpower (Pe) is set to a level at which the recording film is heated to atemperature equal to or higher than the crystallization temperaturethereof and lower than the melting point thereof, thereby performingso-called solid phase erasing.

Here, in a data rewritable type optical recording medium having twoinformation recording layers, since data are recorded or reproduced byfocusing a laser beam onto one of the information recording layers, inthe case of recording data in or reproducing data from the informationrecording layer farther from the light incidence plane (hereinafterreferred to as an “L1 layer”), a laser beam is projected thereonto viathe information recording layer closer to the light incidence plane(hereinafter referred to as an “L0 layer”). Therefore, since it isnecessary for the L0 layer to have a sufficiently high lighttransmittance, it is general to form the recording film included in theL0 layer so as to have a thickness considerably thinner than that of therecording film included in the L1 layer.

In this manner, since the thickness of the recording film included inthe L0 layer is set considerably thinner than that of the recording filmincluded in the L1 layer in a data rewritable type optical recordingmedium having two information recording layers, when data recorded inthe L0 layer is directly overwritten, it is difficult to ensure asufficiently high erasing efficiency. This is because if the recordingfilm is very thin, the phase change material is more stable in theamorphous phase than in the crystal phase and the phase change materialis hard to crystallize by the solid phase erasing, while if therecording film has a thickness equal to or thicker than a predeterminedthickness, since the recording film is more stable in the crystal phasethan in the amorphous phase, a sufficiently high erasing efficiency canbe ensured by the solid phase erasing.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aninformation recording method for recording information in a datarewritable type optical recording medium having a plurality ofinformation recording layers, which method ensures a sufficiently higherasing efficiency when data recorded in any one of the informationrecording layers are directly overwritten.

Further, another object of the present invention is to provide aninformation recording apparatus for recording information in a datarewritable type optical recording medium having a plurality ofinformation recording layers, which apparatus ensures a sufficientlyhigh erasing efficiency when data recorded in any one of the informationrecording layers are directly overwritten.

Moreover, a further object of the present invention is to provide a datarewritable type optical recording medium having a plurality ofinformation recording layers, which medium ensures a sufficiently higherasing efficiency when data recorded in any one of the informationrecording layers are directly overwritten.

The above object of the present invention can be accomplished by aninformation recording method for recording information in a datarewritable type optical recording medium having at least stacked firstand second information recording layers by projecting a laser beamthereonto via a light incidence plane, the information recording methodcomprising steps of recording information in the first informationrecording layer in accordance with an off-pulse recording format andrecording information in the second information recording layer inaccordance with an on-pulse recording format.

In a preferred aspect of the present invention, the first informationrecording layer is located on the side of the second informationrecording layer on which the light incidence plane is present.

In a further preferred aspect of the present invention, each of thefirst and second information recording layers includes a recording filmformed of a phase change material and dielectric layers sandwiching therecording film therebetween and the recording film included in the firstinformation recording layer is thinner than that included in the secondinformation recording layer.

The above object of the present invention can be also accomplished by aninformation recording method for recording information in an opticalrecording medium having at least stacked first and second informationrecording layers containing a phase change material by projecting alaser beam thereonto via a light incidence plane, the informationrecording method comprising steps of recording information in the firstinformation recording layer in accordance with a pulse train pattern bywhich data can be melt erased and recording information in the secondinformation recording layer in accordance with a pulse train pattern bywhich data can be solid phase erased.

The above object of the present invention can be also accomplished by aninformation recording method for recording information in an opticalrecording medium having at least stacked first and second informationrecording layers containing a phase change material by projecting alaser beam thereonto via a light incidence plane, the informationrecording method comprising steps of recording information in the firstinformation recording layer by modulating intensity of the laser beambetween two values and recording information in the second informationrecording layer by modulating intensity of the laser beam between threeor more values.

The above object of the present invention can be also accomplished by aninformation recording apparatus for recording information in a datarewritable type optical recording medium having at least stacked firstand second information recording layers by projecting a laser beamthereonto via a light incidence plane, the information recordingapparatus being constituted so as to record information in the firstinformation recording layer in accordance with an off-pulse recordingformat and record information in the second information recording layerin accordance with an on-pulse recording format.

In a preferred aspect of the present invention, the first informationrecording layer is located on the side of the second informationrecording layer on which the light incidence plane is present.

In a further preferred aspect of the present invention, each of thefirst and second information recording layers includes a recording filmformed of a phase change material and dielectric layers sandwiching therecording film therebetween and the recording film included in the firstinformation recording layer is thinner than that included in the secondinformation recording layer.

The above object of the present invention can be also accomplished by anoptical recording medium which includes at least stacked first andsecond information recording layers and in which information can berecorded by projecting a laser beam thereonto via a light incidenceplane, which optical recording medium comprises setting informationrequired for recording information in the first information recordinglayer in accordance with an off-pulse recording format and recordinginformation in the second information recording layer in accordance withan on-pulse recording format.

In a preferred aspect of the present invention, the first informationrecording layer is located on the side of the second informationrecording layer on which the light incidence plane is present.

In a further preferred aspect of the present invention, each of thefirst and second information recording layers includes a recording filmformed of a phase change material and dielectric layers sandwiching therecording film therebetween and the recording film included in the firstinformation recording layer is thinner than that included in the secondinformation recording layer.

In a further preferred aspect of the present invention, the recordingfilm included in the first information recording layer has a thickness0.3 to 0.8 times that of the recording film included in the secondinformation recording layer.

According to the present invention, a sufficiently high erasingefficiency can be ensured when data recorded in any one of theinformation recording layers are directly overwritten.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section illustrating the structure of anoptical recording medium 10 according to a preferred embodiment of thepresent invention.

FIG. 2 is a drawing illustrating a part of a process (a step for forminga substrate 11) for manufacturing an optical recording medium 10.

FIG. 3 is a drawing illustrating a part of a process (a step for formingan L1 layer 30) for manufacturing an optical recording medium 10.

FIG. 4 is a drawing illustrating a part of a process (a step for forminga transparent intermediate layer 12) for manufacturing an opticalrecording medium 10.

FIG. 5 is a drawing illustrating a part of a process (a step for formingan L0 layer 20) for manufacturing an optical recording medium 10.

FIG. 6 is a set of waveform diagrams showing pulse train patterns usedfor recording data in an L0 recording film 22 of an optical recordingmedium 10, wherein FIG. 6( a) shows a case of recording a 2T signal or a3T signal, FIG. 6( b) shows a case of recording a 4T signal or a 5Tsignal, FIG. 6( c) shows a case of recording a 6T signal or a 7T signaland FIG. 6( d) shows a case of recording an 8T signal.

FIG. 7 is a set of waveform diagrams showing pulse train patterns usedfor recording data in an L1 recording film 32 of an optical recordingmedium 10, wherein FIG. 7( a) shows a case of recording a 2T signal,FIG. 7( b) shows a case of recording a 3T signal, FIG. 7( c) shows acase of recording a 4T signal and FIG. 7( d) shows a case of recordingone of a 5T signal to an 8T signal.

FIG. 8 is a schematic drawing of the major components of an informationrecording apparatus 50 for recording data in an optical recording medium10.

FIG. 9 is a set of waveform diagrams showing pulse train patterns usedfor recording data in an L0 recording film 22 of a DVD type opticalrecording medium, wherein FIG. 9( a) shows a case of recording a 10Tsignal or an 11T signal and FIG. 9( b) shows a case of recording one ofa 12T signal to a 14T signal.

FIG. 10 is a set of waveform diagrams showing pulse train patterns usedfor recording data in an L1 recording film 32 of a DVD type opticalrecording medium, wherein FIG. 10( a) shows a case of recording a 3Tsignal, FIG. 10( b) shows a case of recording a 4T signal, FIG. 10( c)shows a case of recording a 5T signal and FIG. 10( d) shows a case ofrecording one of a 6T signal to a 14T signal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be explained indetail with reference to the drawings.

FIG. 1 is a schematic cross section illustrating the structure of anoptical recording medium 10 according to a preferred embodiment of thepresent invention.

As shown in FIG. 1, an optical recording medium 10 according to thisembodiment includes a substrate 11, an intermediate layer 12, a lighttransmission layer 13, an L0 layer 20 provided between the intermediatelayer 12 and the light transmission layer 13 and an L1 layer 30 providedbetween the substrate 11 and the intermediate layer 12. The L0 layer 20constitutes an information recording layer far from a light incidenceplane 13 a and is constituted by a first dielectric film 21, an L0recording film 22 and a second dielectric film 23. Further, the L1 layer30 constitutes an information recording layer close to the lightincidence plane 13 a and is constituted by a third dielectric film 31,an L1 recording film 32 and a fourth dielectric film 33. In this manner,the optical recording medium 10 according to this embodiment includestwo information recording layers (the L0 layer 20 and the L1 layer 30).

The substrate 11 is a disc-like substrate having a thickness of about1.1 mm serving as a support for ensuring mechanical strength requiredfor the optical recording medium 10 and grooves 11 a and lands 11 b areformed on the surface thereof. The grooves 11 a and/or lands 11 b serveas a guide track for the laser beam L when data are to be recorded inthe L1 layer 30 or when data are to be reproduced from the L1 layer 30.Although the depth of the groove 11 a is not particularly limited, it ispreferably set to 10 nm to 40 nm and the pitch of the grooves 11 a ispreferably set to 0.2 μm to 0.4 μm. Various materials can be used forforming the substrate 11 and the substrate 11 can be formed of glass,ceramic, resin or the like. Among these, resin is preferably used forforming the substrate 11 since resin can be easily shaped. Illustrativeexamples of resins suitable for forming the substrate 11 includepolycarbonate resin, olefin resin, acrylic resin, epoxy resin,polystyrene resin, polyethylene resin, polypropylene resin, siliconeresin, fluoropolymers, acrylonitrile butadiene styrene resin, urethaneresin and the like. Among these, polycarbonate resin or olefin resin ismost preferably used for forming the substrate 11 from the viewpoint ofeasy processing, optical characteristics and the like. In thisembodiment, since the laser beam L does not pass through the substrate11, it is unnecessary for the substrate 11 to have a light transmittanceproperty.

The intermediate layer 12 serves to space the L0 layer 20 and the L1layer 30 apart by a sufficient distance and grooves 12 a and lands 12 bare formed on the surface thereof. The grooves 12 a and/or lands 12 bserve as a guide track for the laser beam L when data are to be recordedin the L0 layer 20 or when data are to be reproduced from the L0 layer20. The depth of the groove 12 a and the pitch of the grooves 12 a canbe set to be substantially the same as those of the grooves 11 a formedon the surface of the substrate 11. The depth of the intermediate layer12 is preferably set to be 10 μm to 50 μm. The material for forming theintermediate layer 12 is not particularly limited and an ultraviolet raycurable acrylic resin is preferably used for forming the intermediatelayer 12. It is necessary for the transparent intermediate layer 12 tohave sufficiently high light transmittance since the laser beam L passesthrough the transparent intermediate layer 12 when data are to berecorded in the L1 layer 30 and data recorded in the L1 layer 30 are tobe reproduced.

The light transmission layer 13 forms an optical path of a laser beamand a light incident plane 13 a is constituted by one of the surfacesthereof. The thickness of the light transmission layer 13 is preferablyset to be 30 μm to 200 μm. The material for forming the lighttransmission layer 13 is not particularly limited and, similarly to theintermediate layer 12, an ultraviolet ray curable acrylic resin ispreferably used for forming the light transmission layer 13. Asdescribed above, it is necessary for the light transmission layer 13 tohave sufficiently high light transmittance since the laser beam L passesthrough the transparent intermediate layer 13.

Each of the L0 recording film 22 and the L1 recording film 32 is formedof a phase change material. Utilizing the difference in the reflectioncoefficients between the case where the L0 recording film 22 and the L1recording film 32 are in a crystal phase and the case where they are inan amorphous phase, data are recorded in the L0 recording film 22 andthe L1 recording film 32. The material for forming the L0 recording film22 and the L1 recording film 32 is not particularly limited but it ispreferable to form them using a SbTe system material. As the SbTe systemmaterial, SbTe may be used alone, or InSbTeGe, AgInSbTe, Ag SbTeGe,AgInSbTeGe or the like containing In, Te, Ge, Ag or the like asadditives may be used.

Since the laser beam passes through the L0 recording film 22 when dataare recorded in the L1 layer 30 and data recorded in the L1 layer 30 arereproduced, it is necessary for the L0 layer 20 to have a high lighttransmittance. Therefore, the thickness of the L0 recording film 22 isset to be considerably thinner than that of the L1 recording film 32.Concretely, it is preferable to set the thickness of the L1 recordingfilm 32 to be about 3 to 20 nm and the thickness of the L0 recordingfilm 22 to be 0.3 to 0.8 times that of the L1 recording film 32.

The first dielectric film 21 and the second dielectric film 23 formed soas to sandwich the L0 recording film 22 serve as protective films forthe L0 recording film 22 and the third dielectric film 31 and the fourthdielectric film 33 formed so as to sandwich the L1 recording film 32serve as protective films for the L1 recording film 32. The thickness ofthe first dielectric film 21 is preferably set to be 2 to 200 nm, thethickness of the second dielectric film 23 is preferably set to be 2 to200 nm, the thickness of the third dielectric film 31 is preferably setto be 2 to 200 nm and the thickness of the fourth dielectric film 33 ispreferably set to be 2 to 200 nm.

Each of these dielectric films may have a single-layered structure ormay have a multi-layered structure including a plurality of dielectricfilms. The material for forming each of these dielectric films is notparticularly limited but it is preferable to form it of oxide, nitride,sulfide, carbide of Si, Al, Ta and Zn such as SiO₂, Si₃O₄, Al₂O₃, AlN,TaO, ZnS, CeO₂ and the like or a combination thereof.

The reflective film 34 serves to reflect the laser beam entering throughthe light incident plane 13 a so as to emit it from the light incidentplane 13 a and the thickness thereof is preferably set to be 20 to 200nm. The material for forming the reflective film 34 is not particularlylimited but the reflective film 34 is preferably formed of an alloycontaining Ag or Al as a primary component and may be formed of Au, Ptor the like. Further, a moisture proof film may be provided between thereflective film 34 and the substrate 11 in order to prevent thereflective film 34 from being corroded. Materials usable for formingeach of the first dielectric film 21 to the fourth dielectric film 33can be used for forming the moisture proof film. Further, although theL0 layer 20 includes no reflective film, a thin reflective film having athickness of about 3 to 15 nm may be provided in the L0 layer 20. Inthis case, the reflective film can be formed of the same material asused for forming the reflective film 34.

When data recorded in the thus constituted optical recording medium 10are reproduced, a laser beam having a wavelength of 200 to 450 nm isprojected onto the optical recording medium 10 via the light incidenceplane 13 a and the amount of the laser beam reflected from the opticalrecording medium 10 is detected. As described above, since the L0recording film 22 and the L1 recording film 32 are formed of the phasechange material and the reflection coefficient in the case where thephase change material is in the crystal phase and that in the case whereit is in the amorphous phase are different from each other, it ispossible to judge by projecting the laser beam via the light incidenceplane 13 a, focusing it onto one of the L0 recording film 22 and the L1recording film 32 and detecting the amount of the laser beam reflectedtherefrom whether a region of the L0 recording film 22 or the L1recording film 32 irradiated with the laser beam is in the crystal phaseor the amorphous phase.

When data are to be recorded in the optical recording medium 10, a laserbeam having a wavelength of 200 to 450 nm is projected to be focusedonto one of the L0 recording film 22 and the L1 recording film 32 and inaccordance with data to be recorded therein, a predetermined region ofone of the L0 recording film 22 and the L1 recording film 32 is heatedto a temperature equal to or higher than the melting point thereof andquickly cooled, thereby changing the phase thereof to the amorphousphase or a predetermined region of one of the L0 recording film 22 andthe L1 recording film 32 is heated to a temperature equal to or higherthan the crystallization temperature and gradually cooled, therebychanging the phase thereof to the crystal phase. The region whose phasehas been changed to the amorphous phase is referred to as “a recordingmark” and recorded data are expressed by the length from the startingpoint of the recording mark to the ending point thereof and the lengthfrom the ending point thereof to the starting point of the nextrecording mark. The length of each recording mark and the length betweenrecording marks (edge to edge) are set to one of the lengthscorresponding to 2T through 8T (where T is the clock period) whenadopting the (1,7) RLL modulation scheme, although this is no particularlimitation. A pulse train pattern used for recording data in the L0recording film 22 and a pulse train pattern used for recording data inthe L1 recording film 32 will be described later.

When recording data in or reproducing data from the L1 layer 30, a laserbeam is projected onto the L1 recording film 32 via the L0 layer 20.Therefore, it is necessary for the L0 layer 20 to have a high lighttransmittance and, as pointed out above, the thickness of the L0recording film 22 is set to be considerably thinner than that of the L1recording film 32.

Here follows a description of the method of manufacturing an opticalrecording medium 10 according to this preferred embodiment.

FIGS. 2 to 5 are step drawings illustrating the method of manufacturingthe optical recording medium 10.

First, as shown in FIG. 2, a stamper 40 is used to perform injectionmolding of a substrate 11 having grooves 11 a and lands 11 b. Next, asshown in FIG. 3, the sputtering method is used to form, upon nearly theentire surface of the side of the substrate 11 on which the grooves 11 aand the lands 11 b are formed, a reflective film 34, a fourth dielectricfilm 33, an L1 recording film 32 and a third dielectric film 34 in thisorder, thereby forming an L1 layer 30. Here, the phase of the L1recording film 32 is normally in an amorphous phase immediately afterthe sputtering is completed.

Next, as shown in FIG. 4, ultraviolet curable acrylic resin isspin-coated onto the L1 layer 30, and by shining an ultraviolet raythrough a stamper 41 in the state with its surface covered with thestamper 41, an intermediate layer 12 having grooves 12 a and lands 12 bis formed. Next, as shown in FIG. 5, the sputtering method is used toform, upon nearly the entire surface of the intermediate layer 12 onwhich the grooves 11 a and the lands 11 b are formed, a seconddielectric film 23, an L0 recording film 22 and a first dielectric film21 in this order. Thus, an L0 layer 20 is completed. Here, the phase ofthe L0 recording film 22 is normally in an amorphous phase immediatelyafter the sputtering is completed.

Moreover, as shown in FIG. 1, ultraviolet curable acrylic resin isspin-coated onto the L0 layer 20, and by shining an ultraviolet ray, alight transmission layer 13 is formed. This completes all filmdeposition steps. In this specification, the optical recording medium inthe state with the film deposition steps complete may also be called the“optical recording medium precursor.”

Next, the optical recording medium precursor is placed upon the rotarytable of a laser irradiation apparatus (not shown) and rotated whilebeing continuously irradiated with a rectangular laser beam having ashorter length in the direction along the track and a longer length inthe direction perpendicular to the track. By shifting the irradiationposition in the direction perpendicular to the track each time theoptical recording medium precursor makes one revolution, the rectangularlaser beam can be shined over nearly the entire surface of the L0recording film 22 and the L1 recording film 32. Thereby, the phasechange material making up the L0 recording film 22 and the L1 recordingfilm 32 is heated to a temperature equal to or higher than thecrystallization temperature thereof and then cooled slowly, so theentire surface of the L0 recording film 22 and the L1 recording film 32is put into the crystalline state, namely the unrecorded state. Thisprocess is called “an initializing process” in this specification.

When the initializing process is completed, the optical recording medium10 is competed.

As described above, it is possible to record the desired digital dataonto an optical recording medium 10 thus manufactured by aligning thefocus of the laser beam during recording to either the L0 recording film22 or the L1 recording film 32 to form recording marks. In addition,when data is recorded onto the L0 recording film 22 and/or L1 recordingfilm 32 of the optical recording medium 10 in this manner, as describedabove, by aligning the focus of a laser beam set to playback power toeither the L0 recording film 22 or the L1 recording film 32 anddetecting the amount of light reflected, it is possible to play back thedigital data thus recorded.

Next, a pulse train pattern used for recording data in the L0 recordingfilm 22 and a pulse train pattern used for recording data in the L1recording film 32 will be described in detail.

Since, as mentioned above, it is necessary to form the L0 recording film22 to be considerably thinner than the L1 recording film 32 and a laserbeam has to be projected onto the L1 recording film 32 via the L0 layer20 when data are to be recorded in the L1 recording film 32, in thisembodiment essentially different pulse train patterns are employedbetween the case of recording data in the L0 recording film 22 and thecase of recording data in the L1 recording film 32.

FIG. 6 is a set of waveform diagrams showing pulse train patterns usedfor recording data in the L0 recording film 22 of an optical recordingmedium 10, wherein FIG. 6( a) shows a case of recording a 2T signal or a3T signal, FIG. 6( b) shows a case of recording a 4T signal or a 5Tsignal, FIG. 6(c) shows a case of recording a 6T signal or a 7T signaland FIG. 6( d) shows a case of recording an 8T signal.

As shown in FIGS. 6( a) to (d), in this embodiment, when data are to berecorded in the L0 recording film 22, a so-called “off-pulse recordingformat” is employed. In the off-pulse recording format, the power of thelaser beam is modulated between two levels (two values) of a recordingpower (Pw0) and a bottom power (Pb0). The recording power (Pw0) is setto such a high level that the L0 recording film 22 can be melted byirradiation with the laser beam and the bottom power (Pb0) is set tosuch a low level that the melted L0 recording film 22 can be cooled evenif it is irradiated with the laser beam. Although the recording powerand the bottom power are not particularly limited, the recording power(Pw0) can be set to about 5 mW and the bottom power (Pb0) can be set toabout 0.1 mW. Here, the values of the recording power (Pw0) and thebottom power (Pb0) are defined as those of the power of the laser beamat the surface of the optical recording medium 10.

When a recording mark is formed using this format, namely, when thephase of the L0 recording film 22 is changed to the amorphous phase, thepower of the laser beam is modulated in accordance with the waveformhaving an amplitude between the recording power (Pw0) and the bottompower (Pb0) and the L0 recording film 22 heated to a temperature equalto or higher than the melting point thereof is quickly cooled. On theother hand, when the recording mark is to be erased, namely, when the L0recording film 22 is to be crystallized, the power of the laser beam isfixed at the recording power (Pw0), thereby gradually cooling the L0recording film 22 heated to a temperature equal to or higher than themelting point thereof. Thus, the recording mark is melt-erased.Hereinafter, concrete pulse train patterns for the respective recordingmarks will be described in detail.

First, as shown in FIG. 6( a), in the case of recording a 2T signal or a3T signal in the L0 recording film 22, the number of “off-pulses” is setto 1. Here, the number of off-pulses is defined as the number of timesthe power of the laser beam is lowered to the bottom power (Pb0). Thepulse width A of the off-pulse is not particularly limited but ispreferably set to 2.6T to 3.0T when recording a 2T signal and set to3.4T to 3.8T when recording a 3T signal. Here, as shown in FIG. 6( a),the pulse width A of the off-pulse means the interval from the time t₁₁at which the power of the laser beam is changed from the recording power(Pw0) to the bottom power (Pb0) to the time t₁₂ at which the power ofthe laser beam is changed from the bottom power (Pb0) to the recordingpower (Pw0).

As a result, at a region where a 2T signal or a 3T signal is to berecorded, the L0 recording film 22 melted by irradiation with the laserbeam of the recording power (Pw0) is quickly cooled during the off-pulseand the phase thereof is changed to the amorphous phase. On the otherhand, at the other regions, the L0 recording film 22 melted byirradiation with the laser beam of the recording power (Pw0) isgradually cooled as the laser beam moves away, thereby beingcrystallized.

Further, as shown in FIG. 6( b), in the case of recording a 4T signal ora 5T signal in the L0 recording film 22, the number of “off-pulses” isset to 2. Here, the pulse widths A and B of the two off-pulses are notparticularly limited but are preferably set to 2.0T to 2.4T whenrecording a 4T signal and set to 2.4T to 2.8T when recording a 5Tsignal. Here, as shown in FIG. 6( b), the pulse width A of the off-pulsemeans the interval from the time t₂₁ at which the power of the laserbeam is first changed from the recording power (Pw0) to the bottom power(Pb0) to the time t₂₂ at which the power of the laser beam is firstchanged from the bottom power (Pb0) to the recording power (Pw0) and thepulse width B of the off-pulse means the interval from the time t₂₃ atwhich the power of the laser beam is second changed from the recordingpower (Pw0) to the bottom power (Pb0) to the time t₂₄ at which the powerof the laser beam is second changed from the bottom power (Pb0) to therecording power (Pw0). Further, the width of a top pulse T_(top) definedas the interval from the time t₂₂ to the time t₂₃ is not particularlylimited but is preferably set to 0.4T to 0.6T.

As a result, at a region where a 4T signal or a 5T signal is to berecorded, the L0 recording film 22 melted by irradiation with the laserbeam of the recording power (Pw0) is quickly cooled during the off-pulseand the phase thereof is changed to the amorphous phase. On the otherhand, at the other regions, the L0 recording film 22 melted byirradiation with the laser beam of the recording power (Pw0) isgradually cooled as the laser beam moves away, thereby beingcrystallized.

Furthermore, as shown in FIG. 6( c), in the case of recording a 6Tsignal or a 7T signal in the L0 recording film 22, the number of“off-pulses” is set to 3. Here, the pulse widths A, B and C of the threeoff-pulses are not particularly limited but are preferably set to 1.6Tto 2.0T when recording a 6T signal and set to 2.0T to 2.4T whenrecording a 6T signal. Here, as shown in FIG. 6( c), the pulse width Aof the off-pulse means the interval from the time t₃₁ at which the powerof the laser beam is first changed from the recording power (Pw0) to thebottom power (Pb0) to the time t₃₂ at which the power of the laser beamis first changed from the bottom power (Pb0) to the recording power(Pw0), the pulse width B of the off-pulse means the interval from thetime t₃₃ at which the power of the laser beam is second changed from therecording power (Pw0) to the bottom power (Pb0) to the time t₃₄ at whichthe power of the laser beam is second changed from the bottom power(Pb0) to the recording power (Pw0), and the pulse width C of theoff-pulse means the interval from the time t₃₅ at which the power of thelaser beam is third changed from the recording power (Pw0) to the bottompower (Pb0) to the time t₃₆ at which the power of the laser beam isthird changed from the bottom power (Pb0) to the recording power (Pw0).Further, the width of a top pulse T_(top) defined as the interval fromthe time t₃₂ to the time t₃₃ and a last pulse T_(lp) defined as theinterval from the time t₃₄ to the time t₃₅ are not particularly limitedbut are preferably set to 0.4T to 0.6T.

As a result, at a region where a 6T signal or a 7T signal is to berecorded, the L0 recording film 22 melted by irradiation with the laserbeam of the recording power (Pw0) is quickly cooled during the off-pulseand the phase thereof is changed to the amorphous phase. On the otherhand, at the other regions, the L0 recording film 22 melted byirradiation with the laser beam of the recording power (Pw0) isgradually cooled as the laser beam moves away, thereby beingcrystallized.

Moreover, as shown in FIG. 6( d), in the case of recording an 8T signalin the L0 recording film 22, the number of “off-pulses” is set to 4.Here, the pulse widths A, B, C and D of the four off-pulses are notparticularly limited but are preferably set to 1.6T to 2.0T. Here, asshown in FIG. 6( d), the pulse width A of the off-pulse means theinterval from the time t₄₁ at which the power of the laser beam is firstchanged from the recording power (Pw0) to the bottom power (Pb0) to thetime t₄₂ at which the power of the laser beam is first changed from thebottom power (Pb0) to the recording power (Pw0), the pulse width B ofthe off-pulse means the interval from the time t₄₃ at which the power ofthe laser beam is second changed from the recording power (Pw0) to thebottom power (Pb0) to the time t₄₄ at which the power of the laser beamis second changed from the bottom power (Pb0) to the recording power(Pw0), the pulse width C of the off-pulse means the interval from thetime t₄₅ at which the power of the laser beam is third changed from therecording power (Pw0) to the bottom power (Pb0) to the time t₄₆ at whichthe power of the laser beam is third changed from the bottom power (Pb0)to the recording power (Pw0), and the pulse width D of the off-pulsemeans the interval from the time t₄₇ at which the power of the laserbeam is fourth changed from the recording power (Pw0) to the bottompower (Pb0) to the time t₄₈ at which the power of the laser beam isfourth changed from the bottom power (Pb0) to the recording power (Pw0).

Further, the width of a top pulse T_(top) defined as the interval fromthe time t₄₂ to the time t₄₃, the width of a multi-pulse T_(mp) definedas the interval from the time t₄₄ to the time t₄₅ and a last pulseT_(lp) defined as the interval from the time t₄₆ to the time t₄₇ are notparticularly limited but are preferably set to 0.4T to 0.6T.

As a result, at a region where an 8T signal is to be recorded, the L0recording film 22 melted by irradiation with the laser beam of therecording power (Pw0) is quickly cooled during the off-pulse and thephase thereof is changed to the amorphous phase. On the other hand, atthe other regions, the L0 recording film 22 melted by irradiation withthe laser beam of the recording power (Pw0) is gradually cooled as thelaser beam moves away, thereby being crystallized.

The pulse train patterns described above are those used for recordingdata in the L0 recording film 22. In this embodiment, in the case ofrecording data in the L0 recording film 22 close to the light incidenceplane 13 a, the so-called off-pulse recording format is employed andrecording marks are melt-erased. It is therefore possible to prevent thephase of a phase change material film having an extremely thin thicknessfrom being returned to the amorphous phase that would be caused bysolid-phase erasing recording marks formed therein. Therefore, since asufficiently high erasing efficiency can be ensured, good overwritingcharacteristics can be obtained.

Next, pulse train patterns used for recording data in the L1 recordingfilm 32 will be described.

FIG. 7 is a set of waveform diagrams showing pulse train patterns usedfor recording data in the L1 recording film 32 of an optical recordingmedium 10, wherein FIG. 7( a) shows a case of recording a 2T signal,FIG. 7( b) shows a case of recording a 3T signal, FIG. 7( c) shows acase of recording a 4T signal and FIG. 7( d) shows a case of recordingone of a 5T signal to an 8T signal.

As shown in FIGS. 7( a) to (d), in this embodiment, when data are to berecorded in the L1 recording film 32, a so-called “on-pulse recordingformat” is employed. In the on-pulse recording format, the power of thelaser beam is modulated between three levels (three values) of arecording power (Pw1), an erasing power (Pe1) and a bottom power (Pb1).The recording power (Pw1) is set to such a high level that the L1recording film 32 can be melted by irradiation with the laser beam, theerasing power (Pe1) is set to such a level that the L1 recording film 32can be heated by irradiation with the laser beam to a temperature equalto or higher than the crystallization temperature thereof and lower thanthe melting point thereof, and the bottom power (Pb1) is set to such alow level that the melted L1 recording film 32 can be cooled even if itis irradiated with the laser beam.

In this case, since the laser beam is projected onto the L1 recordingfilm 32 via the L0 layer 20, the laser beam has been considerablyattenuated when it reaches the L1 recording film 32. Therefore, in orderto sufficiently melt the L1 recording film 32, it is necessary to setthe recording power (Pw1) to be considerably higher than the recordingpower (Pw0) used for recording data in the L0 recording film 22 and itis preferable to set the recording power (Pw1) double the recordingpower (Pw0). Therefore, when the recording power (Pw0) used forrecording data in the L0 recording film 22 is set to about 5.0 mW, therecording power (Pw1) used for recording data in the L1 recording film32 is preferably set to about 10.0 mW. In the case of setting therecording power (Pw1) to about 10.0 mW, it is preferable to set theerasing power (Pe1) to about 4.0 mW and the bottom powe (Pb1) to about0.1 mW, although they are not particularly limited to these values.Here, the values of the recording power (Pw1), the erasing power (Pe1)and the bottom power (Pb1) are defined as those of the power of thelaser beam at the surface of the optical recording medium 10.

When a recording mark is formed using this format, namely, when thephase of the L1 recording film 32 is changed to the amorphous phase, thepower of the laser beam is modulated in accordance with the waveformhaving an amplitude between the recording power (Pw1) or the recordingpower (Pw1) and the bottom power (Pb1), and the L1 recording film 32 isheated to a temperature equal to or higher than the melting pointthereof and is quickly cooled by setting the power of the laser beam tothe bottom power (Pb1). On the other hand, when the recording mark is tobe erased, namely, when the L1 recording film 32 is to be crystallized,the power of the laser beam is fixed at the erasing power (Pe1), therebyheating the L1 recording film 32 to a temperature equal to or higherthan the crystallization temperature thereof and lower than the meltingpoint thereof and gradually cooling the L1 recording film 32. Thus, therecording mark is solid-phase erased. Hereinafter, concrete pulse trainpatterns for the respective recording marks will be described in detail.

First, as shown in FIG. 7( a), in the case of recording a 2T signal inthe L1 recording film 32, the number of “on-pulses” is set to 1 and acooling interval T_(cl) is inserted thereafter. Here, the number ofon-pulses is defined as the number of times the power of the laser beamis raised to the recording power (Pw1). During the cooling intervalT_(cl), the power of the laser beam is set to the bottom power (Pb1).Therefore, in the case of recording a 2T signal, the power of the laserbeam is set to the erasing power (Pe1) before the time t₅₁, set to therecording power (Pw1) during the period (T_(top)) from the time t₅₁ tothe time t₅₂, set to the bottom power (Pb1) during the period (T_(cl))from the time t₅₂ to the time t₅₃ and set to the erasing power (Pe1)after the time t₅₃.

Here, the width T_(top) of a top pulse defined as the interval from thetime t₅₁ to the time t₅₂ is not particularly limited but is preferablyset to 0.3T to 0.5T. The cooling interval T_(cl) defined as the intervalfrom the time t₅₂ to the time t₅₃ is not particularly limited but ispreferably set it to 0.7T to 1.0T.

As a result, at a region where a 2T signal is to be recorded, the L1recording film 32 melted by irradiation with the laser beam of therecording power (Pw1) is quickly cooled during the cooling intervalT_(cl) and the phase thereof is changed to the amorphous phase. On theother hand, at the other regions, the L1 recording film 32 is heated toa temperature equal to or higher than the crystallization temperaturethereof and lower than the melting point thereof and gradually cooled asthe laser beam moves away, thereby being crystallized.

Further, as shown in FIG. 7( b), in the case of recording a 3T signal inthe L1 recording film 32, the number of “on-pulses” is set to 2 and acooling interval T_(cl) is inserted thereafter. Therefore, in the caseof recording a 3T signal, the power of the laser beam is set to theerasing power (Pe1) before the time t₆₁, set to the recording power(Pw1) during the period (T_(top)) from the time t₆₁ to the time t₆₂ andthe period (T_(lp)) from the time t₆₃ to the time t₆₄, set to the bottompower (Pb1) during the period (T_(off)) from the time t₆₂ to the timet₆₃ and the period (T_(cl)) from the time t₆₄ to the time t₆₅, and setto the erasing power (Pe1) after the time t₆₅.

Here, the width T_(top) of a top pulse defined as the interval from thetime t₆₁ to the time t₆₂ is not particularly limited but is preferablyset to 0.3T to 0.5T. The width T_(lp) of a last pulse defined as theinterval from the time t₆₃ to the time t₆₄ is not particularly limitedbut is preferably set to 0.4T to 0.6T. Further, an off interval T_(off)defined as the interval from the time t₆₂ to the time t₆₃ is notparticularly limited but is preferably set to 0.5T to 0.7T. Moreover,the cooling interval T_(cl) defined as the interval from the time t₆₄ tothe time t₆₅ is not particularly limited but is preferably set to 0.7Tto 1.0T.

As a result, at a region where a 3T signal is to be recorded, the L1recording film 32 melted by irradiation with the laser beam of therecording power (Pw1) is quickly cooled during the cooling intervalT_(cl) and the phase thereof is changed to the amorphous phase. On theother hand, at the other regions, the L1 recording film 32 is heated toa temperature equal to or higher than the crystallization temperaturethereof and lower than the melting point thereof and gradually cooled asthe laser beam moves away, thereby being crystallized.

Furthermore, as shown in FIG. 7( c), in the case of recording a 4Tsignal in the L1 recording film 32, the number of “on-pulses” is set to3 and a cooling interval T_(cl) is inserted thereafter. Therefore, inthe case of recording a 4T signal, the power of the laser beam is set tothe erasing power (Pe1) before the time t₇₁, set to the recording power(Pw1) during the period (T_(top)) from the time t₇₁ to the time t₇₂, theperiod (T_(mp)) from the time t₇₃ to the time t₇₄ and the period(T_(lp)) from the time t₇₅ to the time t₇₆, set to the bottom power(Pb1) during the period (T_(off)) from the time t₇₂ to the time t₇₃, theperiod (T_(off)) from the time t₇₄ to the time t₇₅ and the period(T_(cl)) from the time t₇₆ to the time t₇₇, and set to the erasing power(Pe1) after the time t₇₇.

Here, the width T_(top) of a top pulse defined as the interval from thetime t₇₁ to the time t₇₂ is not particularly limited but is preferablyset to 0.3T to 0.5T. Moreover, the width T_(mp) of a multi-pulse definedas the interval from the time t₇₃ to the time t₇₄ is not particularlylimited but is preferably set to 0.3T to 0.5T. Furthermore, the widthT_(lp) of a last pulse defined as the interval from the time t₇₅ to thetime t₇₆ is not particularly limited but is preferably set to 0.4T to0.6T.

Further, an off interval T_(off) defined as the interval from the timet₇₂ to the time t₇₃ and the interval from the time t₇₄ to the time t₇₅is not particularly limited but is preferably to set to 0.5T to 0.7T.Moreover, the cooling interval T_(cl) defined as the interval from thetime t₇₆ to the time t₇₇ is not particularly limited but is preferablyset to 0.7T to 1.0T.

As a result, at a region where a 4T signal is to be recorded, the L1recording film 32 melted by irradiation with the laser beam of therecording power (Pw1) is quickly cooled during the cooling intervalT_(cl) and the phase thereof is changed to the amorphous phase. On theother hand, at the other regions, the L1 recording film 32 is heated toa temperature equal to or higher than the crystallization temperaturethereof and lower than the melting point thereof and gradually cooled asthe laser beam moves away, thereby being crystallized.

Moreover, as shown in FIG. 7( d), in the case of recording any one of a5T signal to an 8T signal in the L1 recording film 32, the number of“on-pulses” is correspondingly set to one of 4 to 7 and a coolinginterval T_(cl) is inserted thereafter. The number of multi-pulses isset to 2 to 5 correspondingly to a 5T signal to an 8T signal. In thiscase, the power of the laser beam is set to the recording power (Pw1)during the period T_(top) from the time t₈₁ to the time t₈₂, the periodsT_(mp) corresponding to those from the time t₈₃ to the time t₈₄, fromthe time t₈₅ to the time t₈₆ and so on and the period T_(lp) from thetime t₈₇ to the time t₈₈, set to the bottom power (Pb1) during the offperiods T_(off) corresponding to those from the time t₈₂ to the timet₈₃, from the time t₈₆ to the time t₈₇ and so on and the coolinginterval T_(cl) from the time t₈₈ to the time t₈₉, and set to theerasing power (Pe1) during the other periods. Further, although thepulse widths are not particularly limited, it is preferable to set thepulse width T_(top) of the top pulse, the pulse width T_(mp) of themulti-pulse and the pulse width T_(lp) of the last pulse to 0.3T to0.5T, 0.3T to 0.5T and 0.4T to 0.6T, respectively, and it is preferableto set the off period T_(off) and the cooling interval T_(cl) to 0.5T to0.7T and 0.7T to 1.0T, respectively.

As a result, at a region where one of a 5T signal to an 8T signal is tobe recorded, the L1 recording film 32 melted by irradiation with thelaser beam of the recording power (Pw1) is quickly cooled during thecooling interval T_(cl) and the phase thereof is changed to theamorphous phase. On the other hand, at the other regions, the L1recording film 32 is heated to a temperature equal to or higher than thecrystallization temperature thereof and lower than the melting pointthereof and gradually cooled as the laser beam moves away, thereby beingcrystallized.

The pulse train patterns described above are those used for recordingdata in the L1 recording film 32. In this manner, in this embodiment, inthe case of recording data in the L1 recording film 32 far from thelight incidence plane 13 a, the so-called on-pulse recording format isemployed and the recording marks are erased using the laser beam havingthe erasing power (Pe1) lower than the recording power (Pw1). It istherefore possible to reduce the load on the laser generating device(semiconductor laser or the like) in comparison with the case whereoff-pulse recording is performed on the L1 recording film 32.

It is preferable to store information for identifying the pulse trainpatterns for the L0 recording film 22 and the L1 recording film 32 as“recording condition setting information” in the optical recordingmedium 10. If such recording condition setting information is stored inthe optical recording medium 10, then when data are actually recorded inthe optical recording medium 10 by the user, the recording conditionsetting information is read by an information recording apparatus andthe pulse train patterns can be determined based on the thus readrecording condition setting information. Therefore, for example, whenthe user requests recording of data in the L0 layer 20, the informationrecording apparatus records data using the pulse train patterns shown inFIG. 6 and when the user requests recording of data in the L1 layer 30,the information recording apparatus records data using the pulse trainpatterns shown in FIG. 7.

It is more preferable for the recording condition setting information toinclude not only information required for identifying the pulse trainpatterns for the L0 recording film 22 and the L1 recording film 32 butalso information required for identifying various conditions such as thelinear recording velocity required to record data in the opticalrecording medium 10. The recording condition setting information may berecorded in the optical recording medium 10 as a wobble signal orpre-pits, or it may be recorded as data in the L0 recording film 22and/or the L1 recording film 32. Further, the recording conditionsetting information may include not only information directly indicatingvarious conditions required to record data but also information capableof indirectly identifying the pulse train patterns by specifying any ofvarious conditions stored in the information recording apparatus inadvance.

FIG. 8 is a schematic drawing of the major components of an informationrecording apparatus 50 for recording data in the optical recordingmedium 10.

As shown in FIG. 8, the information recording apparatus 50 is equippedwith a spindle motor 52 for rotating an optical recording medium 10, anoptical head 53 for shining a laser beam onto the optical recordingmedium 10, a controller 54 for controlling the operation of the spindlemotor 52 and the optical head 53, a laser driving circuit 55 thatsupplies a laser driving signal to the optical head 53, and a lensdriving circuit 56 that supplies a lens driving signal to the opticalhead 53.

Moreover, as shown in FIG. 8, the controller 54 includes a focusingservo circuit 57, a tracking servo circuit 58, and a laser controlcircuit 59. When the focusing servo circuit 57 is activated, the focusis aligned with the recording surface of the rotating optical recordingmedium 10, and when the tracking servo circuit 58 is activated, the spotof the laser beam begins to automatically track the eccentric signaltrack of the optical recording medium 10. The focusing servo circuit 57and tracking servo circuit 58 are provided with an auto gain controlfunction for automatically adjusting the focusing gain and an auto gaincontrol function for automatically adjusting the tracking gain,respectively. In addition, the laser control circuit 59 is a circuitthat generates the laser driving signal supplied by the laser drivingcircuit 55 and generates a laser driving signal based on recordingcondition setting information recorded on the optical recording medium10.

Note that the focusing servo circuit 57, tracking servo circuit 58 andlaser control circuit 59 need not be circuits incorporated in thecontroller 54 but can instead be components separate of the controller54. Moreover, they need not be physical circuits but can instead beaccomplished by software programs executed in the controller 54.

In the case of recording data in the optical recording medium 10 usingthe thus constituted information recording apparatus 50, as describedabove, the recording condition setting information recorded in theoptical recording medium 10 is read and pulse train patterns aredetermined based on the thus read recording condition settinginformation. Therefore, in the case of recording data in the L0 layer20, the information recording apparatus 50 records data using the pulsetrain patterns shown in FIG. 6 based on the thus read recordingcondition setting information and in the case of recording data in theL1 layer 30, the information recording apparatus 50 records data usingthe pulse train patterns shown in FIG. 7 based on the thus readrecording condition setting information.

As described above, in this embodiment, since the off-pulse recordingformat is employed in the case of recording data in the L0 layer 20close to the light incidence plane 13 a and the on-pulse recordingformat is employed in the case of recording data in the L1 layer 30 farfrom the light incidence plane 13 a, even when data recorded in the L0layer 20 are directly overwritten, a sufficiently high erasingefficiency can be ensured and it is possible to reduce the load on thelaser generating device (semiconductor laser or the like).

In the above described embodiment, although explanation was made as tothe case where the present invention was applied to a next-generationtype optical recording medium in which data could be recorded and fromwhich data could be reproduced using a laser beam having a wavelength of200 to 450 nm, the present invention is not limited to such anext-generation type optical recording medium but can be applied to anoptical recording medium such as a DVD in which data can be recorded andfrom which data can be reproduced using a laser beam having a wavelengthof about 650 nm. A preferred embodiment in the case of applying thepresent invention to such an optical recording medium (hereinafterreferred to as “a DVD type optical recording medium”) will be describedin the following.

The DVD type optical recording medium has the essentially sameconfiguration as that of the optical recording medium 10 shown in FIG. 1except for the thicknesses of the substrate 11, the intermediate layer12 and the light transmission layer 13 and the shape of the grooves.Concretely, in the DVD type optical recording medium, the thicknesses ofthe substrate 11, the intermediate layer 12 and the light transmissionlayer 13 are set to 400 to 800 μm, 10 to 100 nm and 30 to 700 μm,respectively, and the depth and pitch of the grooves 11 a (grooves 12 a)are set to 40 to 100 nm and 0.4 to 0.9 μm, respectively.

In the case of recording data in the DVD type optical recording mediumhaving the above identified configuration, a laser beam having awavelength of about 650 nm is focused via the light incidence plane 13 aonto one of the L0 recording film 22 and the L1 recording film 32 andthe phase of a predetermined region of the L0 recording film 22 or theL1 recording film 32 is changed to the crystal phase or the amorphousphase by modulating the power of the laser beam. In this case, the 8/16Modulation Code capable of recording any one of a 3T signal to a 14Tsignal is preferably employed.

As in the above described optical recording medium 10, in the DVD typeoptical recording medium, since it is necessary to set the thickness ofthe L0 recording film 22 to be considerably thinner than that of the L1recording film 32, namely, about 0.3 to 0.8 times that of the L1recording film 32, and to project a laser beam onto the L1 recordingfilm 32 via the L0 recording film 22 when data are to be recorded in theL1 recording film 32, in this embodiment, the off-pulse recording formatis employed in the case of recording data in the L0 recording film 22and the on-pulse recording format is employed in the case of recordingdata in the L1 recording film 32.

FIG. 9 is as set of waveform diagrams showing pulse train patterns usedfor recording data in the L0 recording film 22 in this embodiment,wherein FIG. 9( a) shows a case of recording a 10T signal or an 11Tsignal and FIG. 9( b) shows a case of recording one of a 12T signal to a14T signal. Pulse train patterns used for recording any one of a 3Tsignal to an 8T signal are the same as those shown in FIGS. 6( a) to (d)for recording corresponding signals. Further, in the case of recording a9T signal, the same pulse train pattern for recording an 8T signal shownin FIG. 6( d) is used except that the pulse widths A to D are set to1.8T to 2.2T.

As shown in the diagrams of FIG. 9 (and FIG. 6), in this embodiment,when data are to be recorded in the L0 recording film 22, the off-pulserecording format is employed and the power of the laser beam ismodulated between two levels (two values) of a recording power (Pw0) anda bottom power (Pb0). Although the recording power and the bottom powerare not particularly limited, the recording power (Pw0) can be set toabout 10 mW and the bottom power (Pb0) can be set to about 0.1 mW.

First, as shown in FIG. 9( a), in the case of recording a 10T signal oran 11T signal in the L0 recording film 22, the number of “off-pulses” isset to 5. Here, the pulse widths A, B, C, D and E of five off-pulses arenot particularly limited but are preferably set to 2.0T to 2.4T whenrecording a 10T signal and set to 2.4T to 2.8T when recording an 11Tsignal. As shown in FIG. 9( a), the pulse width A of the off-pulse meansthe interval from the time t₉₁ to the time t₉₂, the pulse width B of theoff-pulse means the interval from the time t₉₃ to the time t₉₄, thepulse width C of the off-pulse means the interval from the time t₉₅ tothe time t₉₆, the pulse width D of the off-pulse means the interval fromthe time t₉₇ to the time t₉₈ and the pulse width E of the off-pulsemeans the interval from the time t₉₉ to the time t₉₁₀.

Further, the width of a top pulse T_(top) defined as the interval fromthe time t₉₂ to the time t₉₃, the width of a multi-pulse T_(mp) definedas the interval from the time t₉₄ to the time t₉₅ and the interval fromthe time t₉₆ to the time t₉₇ and a last pulse T_(lp) defined as theinterval from the time t₉₈ to the time t₉₉ are not particularly limitedbut are preferably set to 0.4T to 0.6T.

Furthermore, as shown in FIG. 9( b), in the case of recording a 12Tsignal to a 14T signal in the L0 recording film 22, the number of“off-pulses” is set to 6. Here, the pulse widths A, B, C, D, E and F ofsix off-pulses are not particularly limited but are preferably set to1.6T to 2.0T when recording a 12T signal, set to 1.8T to 2.2T whenrecording an 13T signal and set to 2.0T to 2.4T when recording an 14Tsignal. As shown in FIG. 9( b), the pulse width A of the off-pulse meansthe interval from the time t₁₀₁ to the time t₁₀₂, the pulse width B ofthe off-pulse means the interval from the time t₁₀₃ to the time t₁₀₄,the pulse width C of the off-pulse means the interval from the time t₁₀₅to the time t₁₀₆, the pulse width D of the off-pulse means the intervalfrom the time t₁₀₇ to the time t₁₀₈, the pulse width E of the off-pulsemeans the interval from the time t₁₀₉ to the time t₁₀₁₀ and the pulsewidth F of the off-pulse means the interval from the time t₁₀₁₁ to thetime t₁₀₁₂.

Further, the width of a top pulse T_(top) defined as the interval fromthe time t₁₀₂ to the time t₁₀₃, the width of a multi-pulse T_(mp)defined as the interval from the time t₁₀₄ to the time t₁₀₅, theinterval from the time t₁₀₆ to the time t₁₀₇ and the interval from thetime t₁₀₈ to the time t₁₀₉, and a last pulse T_(lp) defined as theinterval from the time t₁₀₁₀ to the time t₁₀₁₁ are not particularlylimited but are preferably set to 0.4T to 0.6T.

The pulse train patterns described above are those used for recordingdata in the L0 recording film 22. In this embodiment, in the case ofrecording data in the L0 recording film 22 close to the light incidenceplane 13 a, the so-called off-pulse recording format is employed andrecording marks are melt-erased. It is therefore possible to prevent thephase of a phase change material film having an extremely thin thicknessfrom being returned to the amorphous phase as would be caused bysolid-phase erasing recording marks formed therein. Therefore, since asufficiently high erasing efficiency can be ensured, good overwritingcharacteristics can be obtained.

Next, pulse train patterns used for recording data in the L1 recordingfilm 32 will be described.

FIG. 10 is a set of waveform diagrams showing pulse train patterns usedfor recording data in the L1 recording film 32 in this embodiment,wherein FIG. 10( a) shows a case of recording a 3T signal, FIG. 10( b)shows a case of recording a 4T signal, FIG. 10( c) shows a case ofrecording a 5T signal and FIG. 10( d) shows a case of recording one of a6T signal to a 14T signal.

As shown in FIGS. 10( a) to (d), in this embodiment, when data are to berecorded in the L1 recording film 32, the on-pulse recording format isemployed and the power of a laser beam is modulated between three levels(three values) of a recording power (Pw1), an erasing power (Pe1) and abottom power (Pb1). Although the recording power, the erasing power andthe bottom power are not particularly limited, the recording power (Pw1)can be set to about 14.0 mW, the erasing power (Pe1) can be set to about7.0 mW and the bottom power (Pb1) can be set to about 0.1 mW.

First, as shown in FIG. 10( a), similarly to the case of recording a 2Tsignal in the L1 recording film 32 of the above described opticalrecording medium 10, in the case of recording a 3T signal in the L1recording film 32, the number of “on-pulses” is set to 1 and a coolinginterval T_(cl) is inserted thereafter. Therefore, in the case ofrecording a 3T signal, the power of the laser beam is set to the erasingpower (Pe1) before the time t₁₁₁, set to the recording power (Pw1)during the period (T_(top)) from the time t₁₁₁ to the time t₁₁₂, set tothe bottom power (Pb1) during the period (T_(cl)) from the time t₁₁₂ tothe time t₁₁₃ and set to the erasing power (Pe1) after the time t₁₁₃.

Here, the width T_(top) of a top pulse and the cooling interval T_(cl)are not particularly limited but are preferably set to 0.5T to 0.7T and0.7T to 1.0T, respectively.

Further, as shown in FIG. 10( b), similarly to the case of recording a3T signal in the L1 recording film 32 of the above described opticalrecording medium 10, in the case of recording a 4T signal in the L1recording film 32, the number of “on-pulses” is set to 2 and a coolinginterval T_(cl) is inserted thereafter. Therefore, in the case ofrecording a 4T signal, the power of the laser beam is set to the erasingpower (Pe1) before the time t₁₂₁, set to the recording power (Pw1)during the period (T_(top)) from the time t₁₂₁ to the time t₁₂₂ and theperiod (T_(lp)) from the time t₁₂₃ to the time t₁₂₄, set to the bottompower (Pb1) during the period (T_(off)) from the time t₁₂₂ to the timet₁₂₃ and the period (T_(cl)) from the time t₁₂₄ to the time t₁₂₅, andset to the erasing power (Pe1) after the time t₁₂₅.

Here, the pulse width T_(top) of a top pulse, the pulse width T_(lp) ofa last pulse, an off period T_(of) and the cooling interval T_(cl) arenot particularly limited but are preferably set to 0.3T to 0.5T, 0.4T to0.6T, 0.5T to 0.7T and 0.7T to 1.0T, respectively.

Furthermore, as shown in FIG. 10( c), similarly to the case of recordinga 4T signal in the L1 recording film 32 of the above described opticalrecording medium 10, in the case of recording a 5T signal in the L1recording film 32, the number of “on-pulses” is set to 3 and a coolinginterval T_(cl) is inserted thereafter. Therefore, in the case ofrecording a 5T signal, the power of the laser beam is set to the erasingpower (Pe1) before the time t₁₃₁, set to the recording power (Pw1)during the period (T_(top)) from the time t₁₃₁ to the time t₁₃₂, theperiod (T_(mp)) from the time t₁₃₃ to the time t₁₃₄ and the period(T_(lp)) from the time t₁₃₅ to the time t₁₃₆, set to the bottom power(Pb1) during the period (T_(off)) from the time t₁₃₂ to the time t₁₃₃,the period (T_(off)) from the time t₁₃₄ to the time t₁₃₅ and the period(T_(cl)) from the time t₁₃₆ to the time t₁₃₇, and set to the erasingpower (Pe1) after the time t₁₃₇.

Here, the pulse width T_(top) of a top pulse, the pulse width of amulti-pulse, the pulse width T_(lp) of a last pulse, an off periodT_(of) and the cooling interval T_(cl) are not particularly limited butare preferably set to 0.3T to 0.5T, 0.3T to 0.5T, 0.4T to 0.6T, 0.5T to0.7T and 0.7T to 1.0T, respectively.

Moreover, as shown in FIG. 10( d), in the case of recording any one of a6T signal to a 14T signal in the L1 recording film 32, the number of“on-pulses”is correspondingly set to one of 4 to 12 and a coolinginterval T_(cl) is inserted thereafter. The number of multi-pulses isset to 2 to 10 correspondingly to a 6T signal to a 14T signal. In thiscase, the power of the laser beam is set to the recording power (Pw1)during the period T_(top) from the time t₁₄₁ to the time t₁₄₂, theperiods T_(mp) corresponding to those from the time t₁₄₃ to the timet₁₄₄, from the time t₁₄₅ to the time t₁₄₆ and so on and the periodT_(lp) from the time t₁₄₇ to the time t₁₄₈, set to the bottom power(Pb1) during the off periods T_(off) corresponding to those from thetime t₁₄₂ to the time t₁₄₃, from the time t₁₄₆ to the time t₁₄₇ and soon and the cooling interval T_(cl) from the time t₁₄₈ to the time t₁₄₉,and set to the erasing power (Pe1) during the other periods. Further,although the pulse widths are not particularly limited, it is preferableto set the pulse width T_(top) of the top pulse, the pulse width T_(lp)of the multi-pulse and the pulse width T_(lp) of the last pulse to 0.3Tto 0.5T, 0.3T to 0.5T and 0.4T to 0.6T, respectively, and it ispreferable to set the off period T_(off) and the cooling interval T_(cl)to 0.5T to 0.7T and 0.7T to 1.0T, respectively.

The pulse train patterns described above are those used for recordingdata in the L1 recording film 32. In this manner, in this embodiment, inthe case of recording data in the L1 recording film 32 far from thelight incidence plane 13 a, since the so-called on-pulse recordingformat is employed and the recording marks are erased using the laserbeam having the erasing power (Pe1) lower than the recording power(Pw1), it is possible to reduce load on the laser generating device(semiconductor laser or the like) in comparison with the case where theoff-pulse recording is performed on the L1 recording film 32.

The present invention is in no way limited to the aforementionedembodiments and various modifications are possible within the scope ofthe invention as recited in the claims, and these are naturally includedwithin the scope of the invention.

For example, in the preferred embodiments set out above, an opticalrecording medium having two recording layers was described, but theoptical recording media to which the present invention can be appliedare not limited thereto and the present invention is also applicable tooptical recording media having three or more recording layers. In thiscase, the off-pulse recording format can be employed in the case ofrecording data in at least the information recording layer closest tothe light incidence plane 13 a and the on-pulse recording format can beemployed in the case of recording data in at least the informationrecording layer farthest from the light incidence plane 13 a.

Further, in the preferred embodiments set out above, in the case ofrecording information in the L1 layer 30, the power of the laser beam ismodulated between three levels (three values) of a recording power(Pw1), an erasing power (Pe1) and a bottom power (Pb1). However, it ispossible to record information in the L1 layer 30 by modulating thepower of the laser beam between four values.

As described above, according to the present invention, even when datarecorded in an optical recording medium having a plurality ofinformation recording layers are directly overwritten, a sufficientlyhigh erasing efficiency can be ensured.

1. An information recording method for recording information in a datarewritable type optical recording medium having at least stacked firstand second information recording layers by projecting a laser beamthereonto via a light incidence plane, the information recording methodcomprising steps of recording information in the first informationrecording layer in accordance with an off-pulse recording format andrecording information in the second information recording layer inaccordance with an on-pulse recording format.
 2. An informationrecording method in accordance with claim 1, wherein the firstinformation recording layer is located on the side of the secondinformation recording layer on which the light incidence plane ispresent.
 3. An information recording method in accordance with claim 1,wherein each of the first and second information recording layersincludes a recording film formed of a phase change material anddielectric layers sandwiching the recording film therebetween and therecording film included in the first information recording layer isthinner than that included in the second information recording layer. 4.An information recording method in accordance with claim 2, wherein eachof the first and second information recording layers includes arecording film formed of a phase change material and dielectric layerssandwiching the recording film therebetween and the recording filmincluded in the first information recording layer is thinner than thatincluded in the second information recording layer.
 5. An informationrecording method for recording information in an optical recordingmedium having at least stacked first and second information recordinglayers containing a phase change material by projecting a laser beamthereonto via a light incidence plane, the information recording methodcomprising steps of recording information in the first informationrecording layer in accordance with a pulse train pattern by which datacan be melt erased and recording information in the second informationrecording layer in accordance with a pulse train pattern by which datacan be solid phase erased.
 6. An information recording method forrecording information in an optical recording medium having at leaststacked first and second information recording layers containing a phasechange material by projecting a laser beam thereonto via a lightincidence plane, the information recording method comprising steps ofrecording information in the first information recording layer bymodulating intensity of the laser beam between two values and recordinginformation in the second information recording layer by modulatingintensity of the laser beam between three or more values.
 7. Aninformation recording apparatus for recording information in a datarewritable type optical recording medium having at least stacked firstand second information recording layers by projecting a laser beamthereonto via a light incidence plane, the information recordingapparatus being constituted so as to record information in the firstinformation recording layer in accordance with an off-pulse recordingformat and record information in the second information recording layerin accordance with an on-pulse recording format.
 8. An informationrecording apparatus in accordance with claim 7, wherein the firstinformation recording layer is located on the side of the secondinformation recording layer on which the light incidence plane ispresent.
 9. An information recording apparatus in accordance with claim7, wherein each of the first and second information recording layersincludes a recording film formed of a phase change material anddielectric layers sandwiching the recording film therebetween and therecording film included in the first information recording layer isthinner than that included in the second information recording layer.10. An information recording apparatus in accordance with claim 8,wherein each of the first and second information recording layersincludes a recording film formed of a phase change material anddielectric layers sandwiching the recording film therebetween and therecording film included in the first information recording layer isthinner than that included in the second information recording layer.11. An optical recording medium which includes at least stacked firstand second information recording layers and in which information can berecorded by projecting a laser beam thereonto via a light incidenceplane, which optical recording medium comprises setting informationrequired for recording information in the first information recordinglayer in accordance with an off-pulse recording format and recordinginformation in the second information recording layer in accordance withan on-pulse recording format.
 12. An optical recording medium inaccordance with claim 11, wherein the first information recording layeris located on the side of the second information recording layer onwhich the light incidence plane is present.
 13. An optical recordingmedium in accordance with claim 11, wherein each of the first and secondinformation recording layers includes a recording film formed of a phasechange material and dielectric layers sandwiching the recording filmtherebetween and the recording film included in the first informationrecording layer is thinner than that included in the second informationrecording layer.
 14. An optical recording medium in accordance withclaim 12, wherein each of the first and second information recordinglayers includes a recording film formed of a phase change material anddielectric layers sandwiching the recording film therebetween and therecording film included in the first information recording layer isthinner than that included in the second information recording layer.15. An optical recording medium in accordance with claim 13, wherein therecording film included in the first information recording layer has athickness 0.3 to 0.8 times that of the recording film included in thesecond information recording layer.
 16. An optical recording medium inaccordance with claim 14, wherein the recording film included in thefirst information recording layer has a thickness 0.3 to 0.8 times thatof the recording film included in the second information recordinglayer.